This application claims priority from Japanese patent application No. 2000-293096, filed on Sep. 26, 2000, the complete disclosure of which is hereby incorporated into the patent application by this reference.
The present invention relates to a novel non-drying sealer composition and a process for preparing the same. In particular, the present invention relates to a non-drying sealer composition which is suitable for sealing a gap between a sheet-metal flange and the inside of a trim part by charging the composition into the inside of the trim part of a weatherstrip for an automobile.
The non-drying sealer composition of the present invention will be described by reference to a trunk lid weatherstrip, but can be applied to other weatherstrips for lift gate etc. and to a gap between sheet metals or between a sheet metal and a rubber member.
The general mode of fitting the non-drying sealer is described by reference to the application thereof to a trunk lid weatherstrip (see FIGS. 1 and 2).
FIG. 2 is a sectional view of the fit members along line 2xe2x80x942 in FIG. 1. The weatherstrip 12 is composed of a trim part 14, a hollow sealing part 16 and a sealing lip 18. The trim part 14 is provided with a pair of sandwiching lips 20 and 22 therein and a sheet-metal insert 24 embedded therein for maintaining the shape and sandwiching force thereof.
Sealer S is charged into the grooved bottom of the trim part 14, and via the trim part 14, the weatherstrip 12 is attached to the sheet-metal flange 26 in a trunk. As a result, the sheet-metal flange 26 is inserted into sealer S. In FIG. 2, 27 (chain line) is a trunk lid.
The sealer improves the rust prevention of the sheet-metal flange and the sealing properties of the weatherstrip trim.
As a conventional sealer to be used in such sites, there was the one having a composition shown in e.g. the Reference Example in Table 1.
For the type of sealer shown in Table 1, however, an organic solvent (e.g. kerosine) is essential for dissolving butyl rubber in order to regulate the viscosity in a suitable range.
The organic solvent is generally toxic and highly volatile to cause the following problems.
{circle around (1)} Attention should be paid to maintenance of the working atmosphere during production and application of the sealer, and from the viewpoint of global environmental protection, the discharge (through vaporization) of the solvent to the outside should be prevented as much as possible.
{circle around (2)} For fitting of the sealer, the sealer just after preparation strings highly and thus easily adheres to other parts, thus deteriorating the processability for fitting the sealer, and because of the sagging and running properties of the sealer, a weatherstrip charged with the sealer cannot be turned over in order to attach a sheet-metal flange thereto. On the other hand, the organic solvent is evaporated with time after charging of the sealer to increase the viscosity of the sealer, thus causing the increasing loading upon insertion of sheet metal into the sealer and adversely affecting the processability of fitting the weatherstrip.
Accordingly, the present inventors proposed a non-drying sealer composition which in the absence of an organic solvent, can achieve sealing properties equal to or higher than those of the conventional one (see JP-A 2000-80347), as follows.
xe2x80x9cA non-drying sealer composition comprising liquid rubber as a sealer base, a tackifier and a thixotropic agent as auxiliary materials, and a non-volatile softener or process oil as a dispersing medium.xe2x80x9d
However, the liquid rubber and dispersing medium contained in the non-drying composition described above will swell non-polar vulcanized rubber products such as ethylene propylene-based vulcanized rubber products (vulcanized EPDM rubber products). Accordingly, when the non-drying sealer composition is applied to a weatherstrip made of vulcanized EPDM rubber, the weatherstrip may be deformed and its strength may be decreased resulting in a deterioration in the sealing properties of the weatherstrip. In particular, when the trim part of the weatherstrip is made insert-less, this tendency appears easily and significantly.
In view of the foregoing, the object of the present invention is to provide a non-drying sealer composition which does not substantially swell or shrink non-polar vulcanized rubber products.
The sealer composition of the present invention solves the above problem by the following constitution.
The non-drying sealer composition applied to a non-polar vulcanized rubber product comprises liquid rubber as a sealer base, a tackifier and a thixotropic agent as auxiliary materials, and a non-volatile softener (including a plasticizer) as a dispersing medium, wherein as the non-volatile softer, a shrinking component is used alone or in combination with a swelling component, whereby the swelling action of the sealer composition on the non-polar vulcanized rubber product reaches within about xc2x15% (desirably about 0%) in terms of the degree of swelling.
By constituting the non-drying sealer composition as described above, a product to which the composition has been applied will not swell or shrink, and the product hardly undergo deformation or a reduction in strength. Accordingly, when the composition is applied to a sealing product (e.g. weatherstrip) made of non-polar vulcanized rubber, the deterioration in sealing performance caused by swelling or shrinking of the product hardly occurs.
The shrinking component is preferably a polyether polyol. This is because a polyether polyol having an optimum number of functional groups (OH value) and an optimum molecular weight can be easily obtained from various polyether polyols.
The shrinking component is more preferably a trifunctional polypropylene glycol (PPG). As compared with a bifunctional polyol, the trifunctional PPG has a higher shrinking action and can be selected from a broader range of glycols having various viscosities and molecular weights.
It is preferable in the constitution described above that the liquid rubber is liquid NBR, and the swelling component in the non-volatile softener is a diphthalate-based plasticizer and/or process oil. The diphthalate-based plasticizer and process oil are swelling components, and by combination thereof with a shrinking component such as the above-mentioned polyether polyol e.g. PPG, the swelling action of the sealer composition against the non-polar rubber to which it was applied can easily reaches substantially zero.
As the thixotropic agent, calcium carbonate powder is usually employed. This is because as compared with other thixotropic agents, the calcium carbonate powder is easily available and can easily attain viscosity suitable for charging the sealer composition.